Marine organisms represent an essentially unexploited reservoir for genes and metabolic products of potential biological and/or pharmacological interest [1, 2, 3]. So far, literature on natural products derived from marine organisms is dominated by low molecular weight compounds characterized by cytotoxicity. A number of such natural drugs are either clinically applied or under evaluation as potential anticancer drugs [1, 2, 3]. In contrast, reports on exploitable genes from marine organisms and their products are rare. The green fluorescent protein from the jellyfish Aequorea victoria may serve as an example for a gene of basic biological interest, which is widely used in biotechnology as reporter for studies on gene expression and protein localization in living cells [4].
Sea hares appear to represent another species producing high molecular weight gene products of interest. Originally, the toxicity of the mollusc Aplysia was found to be due to low molecular weight metabolic substances deriving from algal diet [5]. However, cytolytic, antimicrobial and antifungal activities could be detected in biochemical isolates of high molecular weight from the sea hares Aplysia kurodai, Aplysia juliana and Dolabella auricularia. Accordingly it was suggested that these organisms might produce water-soluble gene-expressed biopolymeres of pharmacological interest [5, 6]. Furthermore, these biochemical investigations suggest that sea hares produce a number of closely related glycoproteins of different sizes and with different biological activities. First attempts to characterize these proteins on the sequence level led to the molecular cloning of one Aplysia kurodai-derived cDNA which showed significant sequence identities with the cDNA encoding a protein produced by the giant African snail Achatina fulica [7]. However, a clear correlation of the protein encoded by the cloned Aplysia kurodai cDNA with any biological activity is missing. This is most likely due to the fact that the biologically active molecules are glycoproteins and that recombinant expression in E. coli results in biologically inactive proteins.